The present disclosure relates generally to threaded fasteners that are drivable into a substrate, and more particularly to improved one piece threaded anchors.
Threaded fasteners such as anchors are well known and commercially used throughout the world for securing objects to a variety of substrates. A variety of threaded fasteners can be used to secure objects to concrete, masonry, and other cementitious substrates. Typically, such threaded fasteners include a head, a shank, and a thread formation on the shank for frictionally engaging the substrate into which the fastener is driven. The head typically includes a mechanical engaging structure for engagement by a tool that is used to rotate the threaded fastener and drive the threaded fastener into the substrate.
Often such threaded fasteners are optimally used by pre-drilling the concrete, masonry, or other substrate, for example with a hammer drill equipped with a masonry drill bit. Once the substrate has been pre-drilled, and a correctly sized cavity formed therein, an appropriately sized threaded fastener may be driven or screwed into the substrate to secure an object thereto. One example of such a threaded fastener is described in U.S. Pat. No. 8,322,960 entitled “Threaded Concrete Anchor” and assigned to Illinois Tool Works, Inc. in Glenview, Ill. (who is also the assignee of this patent application). Such fasteners are commercially distributed under the Tapcon® mark, and are sometimes referred to as Tapcon screws or anchors. Tapcon is a registered trademark of Illinois Tool Works, Inc.
Often such threaded fasteners are driven into such a substrate using a powered tool, such as an electric or pneumatic power driving tool or impact driver that imparts a rotational force or torque on the threaded fastener. For example, an impact driver may be fitted with an appropriate bit or socket for engaging the complimentary mechanical engaging structure of the head of the threaded fastener, to rotate the threaded fastener in a tightening direction such that the threads of the threaded fastener engage the substrate. When the threaded fastener is rotated in a tightening direction, the threads of the threaded fastener grip the inside surfaces of the substrate that define the cavity (e.g., the surfaces that define the pre-drilled hole in the substrate), causing the threaded fastener to be driven deeper into the substrate until the head of the threaded fastener comes into contact with either the object being attached by the threaded fastener to the substrate (such as a bracket, flange, clip, or other mechanical device having a hole in it through which the fastener passes). This contact thereby prevents the threaded fastener from being driven, rotated, or tightened further. This results in the threaded fastener being fully tightened and the object being affixed to, secured to, or compressed into contact with the substrate.
Certain problems have arisen due to improvements in electric and pneumatic power driving tools that have caused such tools to become capable of delivering relatively higher levels of torque. When such driving tools are used to drive certain known threaded fasteners, such as those described above, the threaded fasteners can be subjected to relatively large amounts of torque from the rotational forces imparted by these power driving tools. For example, as the threads of the threaded fastener engage the substrate, the threaded fastener experiences frictional resistance forces which tend to impede further driving of the threaded fastener into the substrate. At the same time, the power driving tool is imparting a rotational force or torque on the threaded fastener (typically via the head of the threaded fastener) in an effort to rotate the threaded fastener in a tightening direction and drive it into the substrate. These opposing forces impart significant torsional stresses on the threaded fastener, placing the shank of the threaded fastener under shearing torsional stresses.
These torsional stresses can be so great in various circumstances as to cause the threaded fastener to fail due to the opposing forces or torques placed on the threaded fastener. Over tightening of such threaded fasteners during the driving process is a primary cause of such overstressing of the shank of the threaded fastener, and can result in failure of the threaded fastener due to excessive torsional forces. Threaded fasteners that are subjected to over tightening often fail along the shank, including an upper portion of the shank adjacent to the head of the threaded fastener. Other failures occur at the top of the shank, just under the head of the threaded fastener.
Accordingly, there is a need to provide threaded fasteners that solve these and other problems.